Polyethylene terephthalate resin-coated metal plate of high processability

ABSTRACT

The present invention produces a polyethylene terephthalate resin covered metal sheet having extremely excellent formability, which can be available for uses in which severe forming is practiced such as drawing, drawing and ironing and drawn and stretch forming as well as the composite forming consisting of drawn and stretch forming followed by ironing. A biaxially oriented film consisting of polyethylene terephthalate resin having a low temperature crystallization temperature ranging from 130° C. to 165° C. is covered at least on one side of a metal sheet by heat bonding in the way that the biaxial orientation of the film of the polyethylene terephthalate resin after being covered is gradually increasing from the contacting portion of the film to the metal sheet to the surface portion of the film.

TECHNOLOGICAL FIELD

The present invention relates to polyethylene terephthalate resincovered metal sheet having remarkably excellent formability, which isapplicable to heavily formed use such as drawing, drawing and ironing,drawing and stretch forming, and ironing after drawing and stretchforming.

BACKGROUND OF INVENTION

Metal containers such as beverage can or battery container are formed bydrawing, drawing and ironing, drawing and stretch forming, or ironingafter drawing and stretch forming with the object of material reductionand extension of inside measurement by reduction of wall thickness ofcontainer. These metal containers are generally coated inside to givecorrosion resistance for content and printed after being coated outsideto show content. However, a metal sheet previously covered with organicresin is tried to apply to above-mentioned heavily formed use with aview to reduce coating cost and to eliminate environmental pollutioncaused by dispersing of solvent during coating operation. And cansformed of metal sheet covered with organic resin has already been placedon sale in beverage can market.

In the organic resin covered metal sheet applied to the above-mentionedheavily formed use, a biaxially oriented film, which is manufactured bybiaxial elongation of a thermoplastic polyester resin and subsequentheat-setting of it, is heat bonded to a metal sheet. The biaxialorientation of the film before heat bonding is partially or entirelylost from the contacting portion of the film to the metal sheet to thefree surface (the surface not contacting to the metal sheet) in thethickness direction of the film by the heat conducted from the metalsheet when the film is heat bonded to the metal sheet. When the biaxialorientation of the film is totally lost after heat bonding, it causesthe excellent adhesion between the film and the metal sheet for theabove-mentioned heavily formed use, which is favorable for preventingpeeling-off of the film and generation of film cracks during formingoperation. On the other hand, the film without orientation has so largepermeability that the content permeates the film and corrodes the metalsubstratum, and furthermore, it has faults that coarse spherlites aregenerated in the film by post heating during the operation of printingwhich shows the content or the like and cracks are easily caused in thefilm by falling of container or collision of each container.

Therefore, in the metal sheet covered with polyester resin film havingbiaxial orientation applied to the above-mentioned heavily formed use,the biaxial orientation of the film after the heat bonding is controlledto have formability compatible with permeation resistance and impactresistance (Laid open Japanese patent Hei 6-329669).

So far, copolyester resin obtained by copolymerization of ethyleneterephthalate and ethylene isophthalate has been used in the organicresin covered metal sheet applied to the above-mentioned heavily formeduse, and polyethylene terephthalate without copolymerized component hasnot been used in that field. The following is the reason. That is,copolyester resin obtained by copolymerization of ethylene terephthalateand ethylene isophthalate has small crystallization velocity, whichundergoes little change of biaxial orientation by the temperature changeof the metal sheet when a resin film is covered on a metal sheet by aheat bonding method consisting of contacting a resin film to a metalsheet heated to a temperature more than melting temperature of coveringresin and pressing both, and it is rather easy to make biaxiallyoriented film structure having aforementioned formability compatiblewith permeation resistance and impact resistance by partially losingbiaxial orientation before heat bonding as mentioned before. On theother hand, polyethylene terephthalate has large crystallizationvelocity, which causes extreme difficulty making biaxially oriented filmstructure having aforementioned formability compatible with permeationresistance and impact resistance by partially losing biaxial orientationbefore heat bonding when the film is covered on a metal sheet by heatbonding method. That is, as the biaxial orientation largely changes by alittle temperature change of the metal sheet, it is extremely hard tomake a prescribed film structure after covering. However, as copolyesterresin has small crystallization velocity, it has a fault that crystal isapt to grow into coarse spherlite when it is post heated in theaforementioned printing operation or the like, which causes largerextent of deterioration of impact resistance. Furthermore, the price ofcopolyester resin film is high. Therefore, a polyester resin film ofwhich film structure is easily made into favorable state after heatbonding as that of copolyester resin film and of which price is low isrequired.

THE OBJECTIVE OF THE PRESENT INVENTION

It is the objective of the present invention to produce a polyethyleneterephthalate resin covered metal sheet having extremely excellentformability which can be applied to severely formed use such as drawing,drawing and ironing, drawing and stretch forming, or ironing afterdrawing and stretch forming.

THE METHOD TO REALIZE THE OBJECTIVE OF THE PRESENT INVENTION

Polyethylene terephthalate resin covered metal sheet of the presentinvention is one, wherein a biaxially oriented film consisting ofpolyethylene terephthalate having a low temperature crystallizationtemperature ranging from 130° to 165° C. is covered at least on one sideof a metal sheet by heat bonding, which is characterized by that the lowtemperature crystallization temperature more preferably ranges from 140°to 150° C. It is further characterized by that the biaxial orientationof the polyethylene terephthalate resin film after being covered on themetal sheet by heat bonding is gradually increasing from the contactingportion of the film to the metal sheet to the surface portion of thefilm. And it is still further characterized by that the planarorientation coefficient of the film consisting of the polyethyleneterephthalate resin after being covered on the metal sheet by heatbonding is ranging from 0 to 0.05 (referred as n₁) at the contactingportion of the film to the metal sheet and that is ranging from 0.03 to0.15 (referred as n₂) at the surface portion of the film.

THE BEST MANNER TO PRACTICE THE PRESENT INVENTION

In the present invention, a film which is manufactured by biaxialelongation of poyethylene terephthalate resin having a low temperaturecrystallization temperature ranging 130° to 165° C., more preferably140° to 155° C. is covered on a metal sheet by heat bonding consistingof contacting the resin film to one or either side of the metal sheetheated to a temperature more than melting temperature of the resin,inserting both into a couple of laminating roll, pressing both with thelaminating roll, and quenching both immediately after that. The thusmanufactured polyethylene terephthalate covered metal sheet can beapplied to severely formed use because the biaxial orientation of thefilm is lost at the portion contacting to the metal sheet, which securesexcellent adhesion of the film to the metal sheet, while the biaxialorientation remains higher at the nearer portion to the surface in thethickness direction of the film, which makes orientation structure ofthe film securing excellent permeation resistance and impact resistance.

EMBODIMENT

Hereinafter, the present invention is explained in detail referringembodiment.

At first, the polyethylene terephthalate resin composing the biaxiallyoriented film used in the present invention preferably has a lowtemperature crystallization temperature ranging 130° to 165° C., morepreferably 140° to 155° C. A low temperature crystallization temperatureis explained hereinafter. When an amorphous polyester resin such aspolyethylene terephthalate which is obtained by heating it to atemperature more than melting temperature of it and quenchingimmediately after that is gradually heated using a differential scanningcalorimeter, an exothermic peak appears in the temperature range of 100°to 200° C. depending resin composition. The resin of which exothermicpeak appears in the higher temperature has a smaller crystallizationvelocity, while that appears in the lower temperature has a largercrystallization velocity. For example, the exothermic peak ofpolybutylene terephthalate resin on the market which is heat melted andsubsequently quenched appears at about 50° C., while that ofpolyethylene terephthalate resin on the market which is heat melted andsubsequently quenched appears at about 128° C. On the other hand, incase of ethylene terephthalate-ethylene isophthalate copolyester resin,which is used in a 2 piece can (a can of which body wall part and bottompart is formed in 1 piece) made of a metal sheet covered with apolyester resin film on the market, the exothermic peak appears at about177° C.

In the present invention, a polyethylene terephthalate covered metalsheet having an orientation structure by which adhesion and formabilityare compatible with permeation resistance and impact resistance can beproduced by heat bonding a biaxially oriented film consisting ofpolyethylene terephthalate resin having a low temperaturecrystallization temperature ranging 130° to 165° C. In case where apolyethylene terephthalate resin having a low temperaturecrystallization temperature less than 130° C., the crystallizationvelocity is large, which causes the great change of the biaxialorientation of the film by a slight change of the temperature of themetal sheet during the film covering process. Resultantly, the biaxialorientation widely varies in the film. When the biaxial orientation inthe portion near the metal substratum is not lost enough, peeling-off ofthe film or origination of cracks in the film is caused in the formingof the polyethylene terephthalate resin covered metal sheet and as aresult it can not be formed into a can. On the other hand, when thebiaxial orientation is almost wholly lost in the entire film, thepolyethylene terephthalate resin covered metal sheet can be formed intoa can. However, when a content is packed in such a can and it is storedfor a certain period of time, the content permeates the film andcorrodes the metal substratum, or slight impact to the can causes cracksin the film. That is, When such a resin is used, the temperature rangeof a metal sheet to obtain a polyethylene terephthalate resin coveredmetal sheet having a favorable orientation structure of the film is sonarrow that the operability is extremely poor.

On the other hand, it is extremely difficult in a sense of economy tomanufacture a Homo polymer film consisting of polyethylene terephthalateresin having a low temperature crystallization temperature more than165° C. alone. For this reason, a film having a low temperaturecrystallization temperature more than 165° C. can not but beenmanufactured by adding copolymerization component such as ethyleneisophthalate. In case where this copolyester rein film having a smallcrystallization velocity is covered on a metal sheet under theconditions that formability is compatible with permeation resistance inthe biaxially oriented film after covered on the metal sheet and thusobtained polyester resin covered metal sheet is formed into a can andsubsequently heated, favorable impact resistance is hard to be obtainedsince the copolyester resin film itself is lacking in heat resistance.

The film used in the present invention consisting of polyethyleneterephthalate having a low temperature crystallization temperatureranging 130° to 165° C. is essentially biaxially oriented in order tomeet the above- mentioned characteristics necessary for a can formed ofa metal sheet covered with this film. That is, the polyethyleneterephthalate covered metal sheet of the present invention can be formedinto a favorable can body and the formed can body can have favorablepermeation resistance and impact resistance by changing the biaxialorientation of the film into a favorable orientated structure duringheat bonding.

Furthermore, the thickness of the polyethylene terephthalate resin filmis preferably 5 to 50 μ m, more preferably 10 to 30 μ m. When a film ofwhich thickness is less than 5 μ m is heat bonded to a metal sheet,wrinkles are apt to be caused and it is extremely difficult to stablycover the film on the metal sheet. On the other hand, when using a filmof which thickness is more than 50 μ m, the necessary characteristicscan be attained but it is not profitable to economy.

A colored film, produced by adding color pigment into moltenpolyethylene terephthalate when the film is manufactured, can also beavailable.

Next, a metal sheet used for a polyethylene terephthalate covered metalsheet of the present invention will be explained. A surface treatedstrip or sheet of steel or aluminum alloy is used as a metal sheet. Incase where a steel sheet is used, it is not necessary to define thechemical composition of the steel as far as the aforementioned severeforming can be practiced. The low carbon steel sheet having a thicknessof 0.15 to 0.30 mm is preferably used. In order to produce excellentadhesion after forming of polyethylene terephthalate film to a steelsheet, it is more preferable to use a steel sheet having a coating ofhydrated chromium oxide, a double layered coating consisting of a lowerlayer of metallic chromium and an upper layer of hydrated chromium oxidein particular, on the surface, that is tin free steel (TFS). And thesteel sheet having a plating of one metal selected from tin, nickel oraluminum, a double layered plating or an alloy plating of more than onemetal selected from those 3 metals, and further having theabove-mentioned double layered coating is also available. In case wherean aluminum alloy sheet is used, it is not necessary to define thechemical composition of the aluminum alloy as far as the aforementionedsevere forming can be practiced as with the case of the steel. Thealuminum alloy sheet of JIS 3000 series or 5000 series is preferablyused with a view to economy and formability. It is more preferable touse an aluminum alloy sheet which is surface treated by known methodsuch as the electrolytical treatment or the dipping treatment in thechromic acid solution, the etching in the alkali solution or acidsolution, or the anodic oxidization. In case where the above-mentioneddouble layered coating consisting of a lower layer of metallic chromiumand an upper layer of hydrated chromium oxide is formed on the sheet ofsteel or aluminum, the coating weight of the hydrated chromium oxide ispreferably 3 to 50 mg/m2 as chromium, more preferably 7 to 25 mg/m2 aschromium, on the point of adhesion after forming of the covering resinfilm. It is unnecessary to define the coating weight of the metallicchromium, however, it is preferably 10 to 200 mg/m², more preferably 30to 100 mg/m², on the point of corrosion resistance after forming andadhesion after forming of the covering resin film.

Further next, the covering method of the film of the present inventionconsisting of polyethylene terephthalate resin having low temperaturecrystallization temperature of 130° to 165° C. and biaxial orientationon the above-mentioned metal sheet by heat bonding will be explainedbelow.

The covering method is consisting of

heating a metal strip continuously supplied from a means of the metalstrip supply to the temperature range above the melting temperature ofthe polyethylene terephthalate resin by a heating mean,

contacting a biaxially oriented film of polyethylene terephthalate resinsupplied from a means of the film supply on one side or both sides ofthe metal strip,

putting them together between a couple of laminating roll,

pinching and pressing them, and quenching immediately after that. In theseries of these process, the film of polyethylene terephthalate resin isheated by heat conducted from the metal strip, the polyethyleneterephthalate resin at the contacting portion with the metal stripmelts, and the biaxial orientation of the film is more lost in theportion nearer to the contacting portion with the metal strip, while thebiaxial orientation of the film is more retained in the portion nearerto the uppermost surface free from contacting with the metal strip sincethe uppermost surface of the film, opposite from the contacting surfacewith the metal strip, contacts to the laminating roll which cools thefilm. The orientation structure of the film after covered on the metalstrip changes into more preferable one controlling the temperature ofthe metal strip and the laminating roll, and the period of time duringthe metal strip is contacting to the laminating roll, which correspondsto the feeding speed of the metal strip. The higher temperature of themetal strip and the laminating roll and the greater feeding speed of themetal strip, the greater the film is heated and the more the biaxialorientation of the whole film is lost.

In the covering method mentioned above, in case where the film havingsmall crystallization speed is used, the resin amorphousized by heatingafter the lamination requires longer period of time for therecrystallization, which enables lengthen the period of time from thelamination to the quenching in proportion to the recrystallization speedof the resin, and thus the control of the orientation structure becomesrelatively easier. On the other hand, in case where the film havinggreat crystallization speed is used, the resin amorphousized resinrapidly recrystallizes after the lamination, which requires thequenching immediately after the lamination. As can easily be seen fromthe covering method mentioned above, it is impossible to shorten theperiod of time from the lamination to the quenching below a certainlevel, and the range of the covering process in which the orientation ofthe resin film can be controlled is extremely narrow, which troublescontrolling the film orientation into the required state.

More further next, the orientation structure of the polyethyleneterephthalate resin film after covered on the metal sheet of the presentinvention will be explained below. The biaxial orientation of thepolyethylene terephthalate resin film after covered on the metal sheetis in the state that the biaxial orientation is more lost nearer to thecontacting portion to the metal sheet and it is more retained nearer tothe uppermost surface away from the metal sheet, since the biaxialorientation is destroyed by the heat conducted from the metal sheet whenthe polyethylene terephthalate resin film is contacted and bonded to themetal sheet heated above the melting temperature of the polyethyleneterephthalate resin. In the metal sheet covered with polyethyleneterephthalate resin film of the present invention, the orientationcoefficient of the film portion directly contacting the metal sheet:n₁and that at the uppermost surface of the film: n₂ are preferably 0 to0.05 and 0.03 to 0.15, respectively. In case where the orientationcoefficient of the film portion directly contacting the metal sheet: n₁exceeds 0.05, the covered film is easily peeled off from the surface ofthe metal sheet which is formed into a can body by severe forming at theoutside and the inside of the can body. As the film is not peeled offwhen the orientation coefficient is not more than 0.05, it should becontrolled in the range of 0.05 or less. The polyethylene terephthalateresin at the portion directly contacting to the metal sheet, which ismolten by heating, works the adhesion after forming. The orientationcoefficient of 0 to 0.05 of the polyethylene terephthalate resin at thisportion is enough for the outer side and the inner side of the can body.The measuring method of the orientation coefficient will be explained indetail later. The orientation coefficient that is determined by themeasurement of refractive index is the average value measured at theportion from the lowermost surface of the film peeled off from the metalsheet to the portion 5 μm deep from the surface, which means that evenif the orientation coefficient of the polyethylene terephthalate resinat the portion which had actually contacted to the metal sheet is 0,namely it has no orientation, it is exceeding 0 as far as the portionhaving orientation exists within 5 μm depth. The definition of n₁ as 0to 0.05 in the resin covered metal sheet of the present inventionresults from the consideration mentioned above.

More further next, the orientation coefficient of the polyethyleneterephthalate resin film at the uppermost surface n2 should be in therange of 0.03 to 0.15 from the view point of formability, permeationresistance and impact resistance of the polyethylene terephthalate resincovered metal sheet of the present invention.

In case where the orientation coefficient of the polyethyleneterephthalate resin at the uppermost surface n₂ is less than 0.03, thepermeation resistance of the resin layer itself to the content in thecan remarkably deteriorates, which is unpreferable in particular at thesurface to be the inner surface of the can directly contacting to thepacked content. On the other hand, in case where the orientationcoefficient exceeds 0.15, numerous cracks generates in the polyethyleneterephthalate resin at the uppermost surface by severe forming and sucha can not be a utility article, even if the orientation coefficient ofthe polyester resin portion directly contacting the metal sheet n₁ isless than 0.05. Accordingly, the orientation coefficient of thepolyethylene terephthalate resin at the uppermost surface n 2 should becontrolled in the range of 0.03 to 0.15.

The orientation coefficient of the polyethylene terephthalate resin filmbefore the covering is also an important factor to produce apolyethylene terephthalate resin covered metal sheet. In case where theorientation coefficient exceeds 0.18, when the polyethyleneterephthalate resin film is contacted and bonded to the metal sheetheated to a temperature above the melting temperature of thepolyethylene terephthalate resin, it is extremely hard to control theorientation coefficient of the polyethylene terephthalate resin lessthan 0.15 at the uppermost surface portion and less than 0.05 at theportion where the polyethylene terephthalate resin directly contacts tothe metal sheet. Therefore, the orientation coefficient of thepolyethylene terephthalate resin film before the covering is preferablyless than 0.18, more preferably nearly 0.17.

The orientation coefficient of the polyethylene terephthalate resin filmbefore the covering, and n₁ and n₂ which are those at the portion wherethe resin film directly contacts to the metal sheet and at the uppermostsurface after the covering, respectively, which are all importantfactors in the polyethylene terephthalate resin covered metal sheet ofthe present invention, can be determined by the following method.Namely, the orientation coefficient of the polyethylene terephthalateresin film for use is determined according to the next formula measuringthe refractive indexes in the lengthwise direction, the widthwisedirection and the thickness direction using Abbe's refractometer.

orientation coefficient=(A+B)/2−C

A: refractive index in the lengthwise direction

B: refractive index in the widthwise direction

C: refractive index in the thickness direction

In case of the polyethylene terephthalate resin covered metal sheet, theresin covered metal sheet is immersed in the hydrochloric acid solution,the metal sheet surface is chemically dissolved, and only thepolyethylene terephthalate resin film is peeled off, then followed bymeasuring the refractive indexes of the thus prepared resin film at theportion where the resin film directly contacted to the metal sheet andat the uppermost surface in the lengthwise, the widthwise and thethickness directions in the same manner as mentioned above, and thendetermining the orientation coefficient according to the above-mentionedformula.

In the polyethylene terephthalate resin covered metal sheet of thepresent invention, the orientation coefficient of the covered resin filmshows the degree of the crystalline orientation of the polyethyleneterephthalate resin film, however, it is impossible to determine theorientation coefficient of the optically opaque film added by thepigment or the like into the resin. In such a case, it can be determinedusing X ray diffraction method, IR (infrared ray) method or the like.

The degree of orientation of the polyethylene terephthalate resin filmcan be determined by the measurement of the X ray diffraction intensityof (100) plane as an index, namely the X ray diffraction intensity of(100) plane in case of the diffraction angle 2θ=26°. The X raydiffraction intensity has correlation with the orientation coefficient.Therefore, the preparation of the correlation between the X raydiffraction intensity and the orientation coefficient in the resin filmhaving the same chemical composition without pigment enables todetermine the degree of the crystalline orientation measuring the X raydiffraction intensity of (100) plane, even if the resin film ispigmented one.

The measurement of the degree of the crystalline orientation of thecovered polyethylene terephthalate resin film at the portion nearly 5 μmdeep from the uppermost surface can be practiced setting the permeationdepth of X ray penetrating into the polyethylene terephthalate resinfilm to 5 μm in the measurement of the degree of the crystallineorientation by the above-mentioned X ray diffraction method. A thin filmX ray diffractometer makes the measurement easy. Namely, X ray isprojected at the low angle of incidence to the covered polyethyleneterephthalate resin film. The fixation of diffraction angle 2θ to 26°enables to determine the crystalline orientation at the (100)plane ofthe uppermost surface of the covered polyethylene terephthalate resinfilm. However, the preparation of the correlation between the X raydiffraction intensity and the orientation coefficient in the resin filmhaving the same chemical composition without pigment is also required.Further, in the present invention, the thermosetting resin such as theepoxy resin can be intervened between the polyethylene terephthalateresin film and the metal sheet when the resin film is heat bonded to themetal sheet.

The present invention will be explained more in detail below referringto the examples.

EXAMPLE

The biaxially oriented film having thickness of 25 μm produced frompolyethylene terephthalate resins (shown as PET in Tables) havingvarious low temperature crystallization temperature shown in Table 1 to2 and copolyester resin consisting of 88 mole % of ethyleneterephthalate and 12 mole % of ethylene isophthalate (shown as PETI inTables) were covered by the heat bonding on the conditions shown inTable 1 on both sides of TFS (metallic chromium : 110 mg/m2 and hydratedchromium oxide: 14 mg/m2 as chromium) of Temper DR-10 having thicknessof 0.18 mm. The orientation coefficient of the resin at the portionwhere the resin film directly contacted to the metal sheet and at theuppermost surface on both sides of the thus produced resin covered metalsheets were measured, and then the resin covered metal sheets wereformed using method described below.

At first, the resin covered metal sheets were punched out into circularblanks having a diameter of 160 mm and then they were formed into drawncans having a diameter of 100 mm. After that, they were formed intoredrawn cans having a diameter of 80 mm by redrawing. These redrawn canswere formed into drawn and stretch formed and ironed cans having adiameter of 66 mm by a composite forming consisting of simultaneousdrawn and stretch forming and ironing. This composite forming waspracticed on the conditions that

the clearance between drawing portion, which corresponds to the upperedge part of the can, and ironing portion was 20 mm,

curvature radius in a corner of dies for redrawing process was 1.5 timesof the thickness of the resin covered metal sheet,

the clearance between the redrawing dies and the punch was 1.0 time ofthe thickness of the resin covered metal sheet, and

the clearance between the ironing portion of the redrawing dies and thepunch was 50% of the thickness of the resin covered metal sheet. Afterthat, the upper edge part of the can was trimmed off by a known method,then they were practiced by necked-in forming and flange forming. Thepeeling-off of the resin layer at the wall portion of the thus producedcan body was evaluated by the method described below. And further, theimpact resistance of the resin film on the inside of the can body wasevaluated by the method described below after baking at 220° C. for 30seconds for that produced from the polyethylene terephthalate resincovered metal sheet and at 210° C. for 30 seconds for that produced fromthe copolyester resin covered metal sheet.

(I) Peeling-off of the resin layer from the can wall portion

The degree of peeling-off of the resin layer from the can wall portionof the inside and outside of the produced can body was observed by thenaked eye and evaluated based on the following standard.

⊚: no peeling-off

∘: slightly peeled off but no problem for practical use

Δ: heavily peeled off

X: peeled off at the whole upper portion of the can body

(II) Impact resistance of the resin film on the inside of the can body

At first, water was packed in the produced can and the rid was corked.Then, the can was fallen on the bottom down from a height of 15 cm.After it was opened and the water was taken out, 3% sodium chloridesolution was packed and a rod of stainless steel as a cathode wasimmersed in it. After that, a voltage about 6.3 volts was chargedbetween the cathode and the can body as an anode. In case where even ifthe metal substratum under the resin layer is slightly exposed, acurrent flows. The degree of the metal expose was evaluated by thecurrent value (mA). The results of the evaluation were shown in Table 3to 4 in accompany with the orientation coefficient of the film of theresin covered metal sheet measured before the forming.

TABLE 1 Characteristics of polyester resins and laminating conditions(1) Covering conditions of resin film Heating Temper- Period of Resinfilm temper- Supply ature time from L.T.C.* ature speed of laminationResin temper- of metal of metal laminat- to Sample compo- ature sheetsheet ing quenching number sition (° C.) (° C.) (m/min) (° C.) (second)1 PET 128 280 200 150 0.5 2 PET 128 290 200 150 0.5 3 PET 128 300 200150 0.5 4 PET 130 270 200 150 0.5 5 PET 130 280 200 150 0.5 6 PET 130290 200 150 0.5 7 PET 140 270 200 150 0.5 8 PET 140 280 200 150 0.5 9PET 140 290 200 150 0.5 Remarks: L.T.C.* Low temperature crystallization

TABLE 2 Characteristics of polyester resins and laminating conditions(2) Covering conditions of resin film Heating Temper- Period of Resinfilm temper- Supply ature time from L.T.C.* ature speed of laminationResin temper- of metal of metal laminat- to Sample compo- ature sheetsheet ing quenching number sition (° C.) (° C.) (m/min) (° C.) (second)10 PET 155 270 200 150 0.5 11 PET 155 280 200 150 0.5 12 PET 155 290 200150 0.5 13 PET 165 270 200 150 0.5 14 PET 165 280 200 150 0.5 15 PET 165290 200 150 0.5 16 PETI 177 235 200 150 0.5 17 PETI 177 245 200 150 0.518 PETI 177 255 200 150 0.5 Remarks: L.T.C.* Low temperaturecrystallization

TABLE 3 Evaluation result of characteristics of resin covered metalsheet (1) Orientation coefficient Evaluation of covered Orientation offilm after covering metal sheet coefficient contacting uppermostPeeling- of film side with surface off of Impact Sample before metalsheet side film (by resistance number covering (n¹) (n²) naked eye) (mA)Item 1 0.1721 0.078 0.158 X 0.00 Comp. Ex.^(#) 2 0.1721 0.041 0.112 Δ0.02 Comp. Ex.^(#) 3 0.1721 0.009 0.067 ⊚ 0.69 Comp. Ex.^(#) 4 0.11580.028 0.076 ◯ 0.00 Example 5 0.1158 0.013 0.046 ⊚ 0.00 Example 6 0.11580.005 0.032 ⊚ 0.04 Example 7 0.1107 0.024 0.071 ◯ 0.00 Example 8 0.11070.011 0.042 ⊚ 0.00 Example 9 0.1107 0.004 0.030 ⊚ 0.02 Example Remarks:Comp. Ex.^(#) Comparative Example

TABLE 4 Evaluation result of characteristics of resin covered metalsheet (2) Orientation coefficient Evaluation of covered Orientation offilm after covering metal sheet coefficient contacting uppermostPeeling- of film side with surface off of Impact Sample before metalsheet side film (by resistance number covering (n¹) (n²) naked eye) (mA)Item 1 0.1123 0.024 0.070 ◯ 0.00 Example 2 0.1123 0.011 0.052 ⊚ 0.00Example 3 0.1123 0.004 0.039 ⊚ 0.00 Example 4 0.1158 0.021 0.067 ◯ 0.00Example 5 0.1158 0.009 0.043 ⊚ 0.01 Example 6 0.1158 0.002 0.031 ⊚ 0.07Example 7 0.1223 0.041 0.112 Δ 0.00 Comp. Ex.^(#) 8 0.1223 0.011 0.074 ⊚0.23 Comp. Ex.^(#) 9 0.1223 0.009 0.067 ⊚ 0.83 Comp. Ex.^(#) Remarks:Comp. Ex.^(#) Comparative Example

As can be seen in Table 3 to 4, the metal sheet covered with apolyethylene terephthalate resin film having a low temperaturecrystallization temperature of 130° to 165° C. of the present inventionis superior in the adhesion after forming and the impact resistance to ametal sheet covered with a polyethylene terephthalate resin film havinga low temperature crystallization temperature lower than that of thepresent invention or that covered with a polyester resin film having alow temperature crystallization temperature higher than that of thepresent invention.

EFFECT OF INVENTION

In the polyethylene terephthalate resin covered metal sheet of thepresent invention,

a biaxially oriented film consisting of polyethylene terephthalate resinhaving a low temperature crystallization temperature ranging from 130°to 165° C. is covered at least on one side of a metal sheet by heatbonding, and

the biaxial orientation of the film of the polyethylene terephthalateresin after being covered on said metal sheet is gradually increasingfrom the contacting portion of the film to said metal sheet to thesurface portion of the film, and further

a planar orientation coefficient of said film consisting of saidpolyethylene terephthalate resin after being covered on said metal sheetis ranging from 0 to 0.05 (n₁) at the contacting portion of said film tosaid metal sheet and that is ranging from 0.03 to 0.15 (n₂) at thesurface portion of said film. Therefore, the adhesion and theformability can be compatible with the permeation resistance and theimpact resistance in the resin covered metal sheet of the presentinvention, and it can be available for uses in which severe forming ispracticed such as drawing, drawing and ironing and drawn and stretchforming as well as the composite forming consisting of drawn and stretchforming followed by ironing.

What is claimed is:
 1. Polyethylene terephthalate resin covered metalsheet, wherein a biaxially oriented film consisting of polyethyleneterephthalate having a low temperature crystallization temperatureranging from 130° to 165° C. is covered at least on one side of a metalsheet by heat bonding.
 2. Polyethylene terephthalate resin covered metalsheet according to claim 1, wherein a low temperature crystallizationtemperature ranges from 140° to 150° C.
 3. Polyethylene terephthalateresin covered metal sheet according to claim 1, wherein a biaxialorientation of a film of said polyethylene terephthalate resin afterbeing covered on said metal sheet by heat bonding is graduallyincreasing from the contacting portion of said film to said metal sheetto the surface portion of said film.
 4. Polyethylene terephthalate resincovered metal sheet according to 3, wherein a planar orientationcoefficient of said film consisting of polyethylene terephthalate resinafter being covered on said metal sheet by heat bonding is ranging from0 to 0.05 (hereinafter referred as n₁) at the contacting portion of saidfilm to said metal sheet and that is ranging from 0.03 to 0.15(hereinafter referred as n₂) at the surface portion of said film. 5.Polyethylene terephthalate resin covered metal sheet, wherein abiaxially oriented film consisting of polyethylene terephthalate havinga low temperature crystallization temperature ranging from 130° to 165°C. is covered at least on one side of a metal sheet by heat bonding, anda biaxial orientation of said film of polyethylene terephthalate resin,after being covered on said metal sheet by heat bonding, is graduallyincreasing from the contacting portion of said film to said metal sheetto the surface portion of said film.
 6. Polyethylene terephthalate resincovered metal sheet according to claim 5, wherein a low temperaturecrystallization temperature ranges from 140° to 150° C.
 7. Polyethyleneterephthalate resin covered metal sheet according to claim 5, wherein abiaxially oriented film consisting of polyethylene terephthalate havinga low temperature crystallization temperature ranging from 130° to 165°C. is covered at least on one side of a metal sheet by heat bonding, anda planar orientation coefficient of said film, consisting ofpolyethylene terephthalate resin, after being covered on said metalsheet by heat bonding, ranges from 0 to 0.05 (hereinafter referred asn₁) at the contacting portion of said film to said metal sheet andranges from 0.03 to 0.15 (hereinafter referred as n₂) at the surfaceportion of said film.
 8. Polyethylene terephthalate resin covered metalsheet according to claim 7, wherein a low temperature crystallizationtemperature ranges from 140° to 150° C.